Systems and methods for producing fuel from a renewable feedstock

ABSTRACT

Methods and systems are provided for producing a fuel from a renewable feedstock. The method includes deoxygenating the renewable feedstock in a deoxygenation zone to produce hydrocarbons with normal paraffins. The hydrocarbons with normal paraffins are isomerized to produce hydrocarbons with branched paraffins. The hydrocarbons with branched paraffins are fractionated to produce a naphtha at a naphtha outlet, where the naphtha is further isomerized.

TECHNICAL FIELD

The present disclosure generally relates to systems and methods forproducing fuels from renewable feedstocks, and more particularly relatesto systems and methods for converting renewable feedstocks into branchedparaffins useful as fuel.

BACKGROUND

Many existing processes for converting renewable feedstocks into dieselfuels or jet fuels produce a naphtha stream as a co-product. The naphthastream often includes many normal paraffin compounds, which are straightchain paraffins, that have a relatively low octane value. The octanevalue can be increased by isomerizing the normal paraffins into branchedparaffins, because branched paraffins produce higher octane values.Increasing the octane value of the naphtha stream increases the value ofthe naphtha stream, and a more valuable naphtha stream increases thevalue of the overall process for converting renewable feedstocks intofuel.

Accordingly, it is desirable to develop methods and systems forincreasing the degree of isomerization of naphtha produced as aco-product with other fuels from renewable feedstocks. In addition, itis desirable to develop methods and systems for increasing the octanevalue of naphtha produced from renewable feedstocks. Furthermore, otherdesirable features and characteristics of the present embodiment willbecome apparent from the subsequent detailed description and theappended claims, taken in conjunction with the accompanying drawings andthis background.

BRIEF SUMMARY

A method is provided for producing fuel from renewable feedstocks. Therenewable feedstock is deoxygenated in a deoxygenation zone to producehydrocarbons with normal paraffins. The hydrocarbons with normalparaffins are isomerized to produce hydrocarbons with branchedparaffins. The hydrocarbons with branched paraffins are fractionated toproduce a naphtha at a naphtha outlet, where the naphtha is furtherisomerized.

Another method is provided for producing a fuel from a renewablefeedstock. The renewable feedstock is contacted with a deoxygenationcatalyst to produce hydrocarbons with normal paraffins. The hydrocarbonswith normal paraffins are contacted with an isomerization catalyst toproduce hydrocarbons with branched paraffins. The hydrocarbons withbranched paraffins are fractionated to produce a naphtha at a naphthaoutlet, and the naphtha is then isomerized.

A system is also provided for producing a fuel from a renewablefeedstock. The system includes a renewable feedstock feed system coupledto a deoxygenation reaction zone. A first isomerization reaction zone iscoupled to the deoxygenation reaction zone, and a fractionation zone iscoupled to the first isomerization reaction zone. The fractionation zoneincludes a naphtha outlet, and the naphtha outlet is coupled to anisomerization reactor.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will hereinafter be described in conjunction withthe following figures, wherein like numerals denote like elements, andwherein:

FIG. 1 is a schematic diagram of an exemplary embodiment of a system andmethod for producing fuel from a renewable feedstock; and

FIG. 2 is a schematic diagram illustrating an exemplary embodiment of asystem and method for fractionating and isomerizing fuel productsproduced from a renewable feedstock.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the application or uses of the embodimentdescribed. Furthermore, there is no intention to be bound by any theorypresented in the preceding technical field, background, brief summary,or the following detailed description.

Various processes for converting renewable feedstocks into fuels,especially into diesel fuel or jet fuel, also produce a naphthaco-product. The naphtha co-product is primarily hydrocarbon moleculeswith 5 to 8 carbon atoms and boils at a lower temperature than diesel orjet fuel. The naphtha co-product could be used for gasoline or otherfuels, but it has a significant component of straight chain (normal)paraffins that have a low octane value. The octane value of the naphthais increased by isomerizing the normal paraffins to produce branchedparaffins, and the higher octane value increases the monetary value ofthe naphtha co-product.

Reference is now made to the exemplary embodiment illustrated in FIG. 1.A renewable feedstock 10 is processed to produce various types of fuel,such as diesel fuel, jet fuel, gasoline, liquid propane gas (LPG), etc.The term renewable feedstock 10 is meant to include feedstocks otherthan those derived from petroleum crude oil, and includes oils extractedfrom plants or animals. The renewable feedstocks 10 as contemplatedherein are any of those which include glycerides or free fatty acids(FFA). Most of the glycerides will be triglycerides, but monoglyceridesand diglycerides may be present and processed as well. Examples of theserenewable feedstocks 10 include, but are not limited to, canola oil,corn oil, rapeseed oil, soybean oil, colza oil, tall oil, sunflower oil,hempseed oil, olive oil, linseed oil, coconut oil, castor oil, peanutoil, palm oil, mustard oil, camelina oil, pennycress oil, tallow, yellowand brown greases, lard, train oil, jatropha oil, fats in milk, fishoil, algal oil, sewage sludge, and the like. Additional examples ofrenewable feedstocks 10 include non-edible vegetable oils, such as oilsfrom Madhuca indica (mahua), Pongamia pinnata, and Azadirachta indica(neem).

The glycerides and FFAs of the typical vegetable or animal fat containaliphatic hydrocarbon chains in their structure which have about 8 toabout 24 carbon atoms. The majority of the fats and oils contain highconcentrations of fatty acids with 16 to 18 carbon atoms, and many typesof oils contain aliphatic hydrocarbon chains within a limited range,such as 14 to 18. Only a limited number of oil types include aliphatichydrocarbon chains covering the entire range from about 8 carbon atomsto about 24 carbon atoms, so the 8 to 24 carbon atoms range is meant toencompass mixtures of all types of oils. Co-feeds, or mixtures ofrenewable feedstocks 10 and petroleum derived hydrocarbons, may also beused as the feedstock. Other feedstock components that may be used,especially as a co-feed component in combination with the above listedfeedstocks, include spent motor oils and industrial lubricants; usedparaffin waxes; liquid derived from the gasification of coal, biomass,or natural gas followed by a downstream liquefaction step such asFischer-Tropsch technology; liquids derived from depolymerization(thermal or chemical) of waste plastics such as polypropylene, highdensity polyethylene, and low density polyethylene; and other syntheticoils generated as byproducts from petrochemical and chemical processes.Mixtures of the above feedstocks may also be used as co-feed components.One advantage of using a co-feed component is the transformation of whatmay have been a waste product into a valuable co-feed component to thecurrent process.

The renewable feedstock 10 is stored and delivered for processing by arenewable feedstock feed system 12. In an exemplary embodiment, therenewable feedstock feed system 12 includes a renewable feedstockstorage tank 14, renewable feedstock pump 16, and associated piping. Therenewable feedstock feed system 12 delivers a renewable feedstock feedstream 18 for further processing. Other embodiments of the renewablefeedstock feed system 12 exist, such as a pipeline from a differentsource, and a pressurized renewable feedstock storage tank 14 without arenewable feedstock pump 16.

Many renewable feedstocks 10 that can be used herein contain a varietyof impurities. For example, tall oil is a byproduct of the woodprocessing industry, and includes esters and rosin acids in addition toFFAs. Rosin acids are cyclic carboxylic acids. The renewable feedstocks10 may also contain contaminants such as alkali metals, (e.g. sodium andpotassium), phosphorous, various solids, water, and detergents. In someembodiments, the renewable feedstock 10 is pre-cleaned in an optionalpre-cleaning zone 20 to improve downstream processing operations, andseveral different types of pre-cleaning are possible. For example, thepre-cleaning zone 20 may be configured to provide a mild acid wash bycontact with dilute sulfuric, nitric, citric, phosphoric, orhydrochloric acid in a reactor. The acid wash can be a continuousprocess or a batch process, and the dilute acid contact can be atambient temperature and atmospheric pressure. Other possiblepre-cleaning steps include, but are not limited to, contacting therenewable feedstock 10 with an ion exchange resin such as Amberlyst®-15,subjecting the renewable feedstock 10 to a caustic treatment, bleachingthe renewable feedstock 10 with an adsorbent, filtration, solventextraction, hydro processing, or combinations of the above.

In some embodiments, a sulfiding agent 22 is added to the renewablefeedstock 10. Several reactors described more fully below use catalystsof various types, and one or more of these catalysts can be used in asulfided state in various embodiments. Sulfur is added to the process tomaintain the catalysts in the sulfided state. The sulfiding agent 22 isadded at a sulfiding agent inlet 24. The sulfur is measured as elementalsulfur, regardless of the compound containing the sulfur, and can beadded in many forms. For example, suitable sulfiding agents 22 include,but are not limited to, dimethyl disulfide, dibutyl disulfide, andhydrogen sulfide. The sulfur may be obtained from various sources, suchas part of a hydrogen stream from a hydrocracking unit or hydro treatingunit, or sulfur compounds removed from kerosene or diesel, and disulfideoils removed from sweetening units such as Merox® units. A deoxygenationcatalyst is described more fully below, and sulfur concentrations ofless than 2,000 ppm are typically sufficient to maintain thedeoxygenation catalyst and the other catalysts described below in asulfided state. FIG. 1 illustrates adding the sulfiding agent 22 to therenewable feedstock feed stream 18, but other embodiments are possible.For example, some renewable feedstocks 10 contain sufficient sulfur tomaintain the catalysts in a sulfided state. Sulfur can also be added tothe renewable feedstock storage tank 14, the reactors containing thecatalysts, or other locations.

In an exemplary embodiment, a recycle hydrogen stream 80 (described morefully below) is added to the renewable feedstock feed stream 18 andflows downstream to a guard bed 26. A portion of a hot separator bottomsstream 50 (described more fully below) is also added to the renewablefeedstock feed stream 18 before entry into the guard bed 26. The guardbed 26 removes metals from the renewable feedstock 10 by contacting therenewable feedstock feed stream 18 with a guard bed catalyst 28 atpretreatment conditions. The guard bed catalyst 28 may initiate adeoxygenation reaction of the renewable feedstock feed stream 18 to somedegree, as described more fully below. In some embodiments, the guardbed catalyst 28 is alumina, either with or without demetallationcatalysts such as nickel or cobalt, but other guard bed catalysts 28 arealso possible. The guard bed 26 is operated at a temperature from about40° C. to about 400° C., for example from about 150° C. to about 300° C.Operating pressures for the guard bed 26 are from about 690 kilopascals(kPa) absolute (100 pounds per square inch absolute (psia)) to about13,800 kPa absolute (2,000 psia), for example from about 1,380 kPaabsolute (200 psia) to about 6,900 kPa absolute (1,000 psia). A portionof the hot separator bottoms stream 50 may be added at various locationsin the guard bed 26 to aid in temperature control, hydrogen solubility,or other purposes, but in other embodiments different streams or nostreams are added at side locations in the guard bed 26.

After the optional guard bed 26, a guard bed effluent 30 flowsdownstream to a deoxygenation reaction zone 40 including one or morecatalyst beds in one or more reactors. In the deoxygenation reactionzone 40, the guard bed effluent 30 is contacted with a deoxygenationcatalyst 42 (sometimes referred to as a hydrotreating catalyst) in thepresence of hydrogen at deoxygenation conditions. The hydrogen for thisreaction is provided from the recycle hydrogen stream 80 added to therenewable feedstock feed stream 18. Under these conditions, the olefinicor unsaturated portions of n-paraffinic chains are hydrogenated.Additionally, any deoxygenation reactions that did not take place in theguard bed 26 are completed in the deoxygenation reaction zone 40. Insome embodiments, a portion of the hot separator bottoms stream 50 isadded at various locations in the deoxygenation reaction zone 40 to aidin temperature control, hydrogen solubility, and other purposes. Inother embodiments, streams other than the hot separator bottoms stream50 (or even no streams) are added at side locations in the deoxygenationreaction zone 40. A deoxygenation effluent 44 exits the deoxygenationreaction zone 40.

Deoxygenation catalysts 42 are any of those well known in the art, suchas nickel, nickel/molybdenum, or cobalt/molybdenum dispersed on a highsurface area support. Other deoxygenation catalysts 42 include one ormore noble metal catalytic elements dispersed on a high surface areasupport. Non-limiting examples of noble metals include platinum (Pt)and/or palladium (Pd). Deoxygenation conditions include a temperature ofabout 40 degrees centigrade (° C.) to about 400° C., and a pressure ofabout 690 kilopascals (kPa) absolute (100 psia) to about 13,800 kPaabsolute (2,000 psia). In another embodiment the deoxygenationconditions include a temperature of about 200° C. to about 300° C., anda pressure of about 1,380 kPa absolute (200 psia) to about 6,900 kPaabsolute (1,000 psia). Other operating conditions for the deoxygenationreaction zone 40 can also be used. A sulfiding agent 22, such as fromthe sulfiding agent inlet 24 or from the renewable feedstock 10,maintains the deoxygenation catalyst 42 in a sulfided state.

The deoxygenation catalysts 42 discussed above are also capable ofcatalyzing decarboxylation, decarbonylation and/or hydrodeoxygenation ofthe renewable feedstock 10 to remove oxygen. Decarboxylation,decarbonylation, and hydrodeoxygenation are herein collectively referredto as “deoxygenation reactions”, and the deoxygenation reactions and theolefin hydrogenation reactions simultaneously occur in the deoxygenationreaction zone 40. Deoxygenation conditions include a relatively lowpressure of about 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia),a temperature of about 200° C. to about 400° C., and a liquid hourlyspace velocity of about 0.2 to about 10 hr⁻¹. In another embodiment thedeoxygenation conditions include the same relatively low pressure ofabout 3,450 kPa (500 psia) to about 6,900 kPa (1,000 psia), atemperature of about 290° C. to about 350° C., and a liquid hourly spacevelocity of about 1 to about 4 hr⁻¹.

Deoxygenation is an exothermic reaction, so the temperature in thedeoxygenation reaction zone 40 increases as the hydrocarbons from therenewable feedstock 10 pass through. Decarboxylation andhydrodeoxygenation reactions begin to occur as the temperatureincreases. The rate of the deoxygenation reactions increases from thefront of the bed to the back of the bed as the temperature increases.The deoxygenation reaction zone 40 can include one or more reactors inseries, and can also include parallel reactors or sets of reactors.

The hydrodeoxygenation reaction consumes hydrogen and produces water asa byproduct, while the decarbonylation and decarboxylation reactionsproduce carbon monoxide (CO) or carbon dioxide (CO₂) without consuminghydrogen. However, hydrogen is present for all the reactions in thedeoxygenation reaction zone 40, regardless of whether the reactionconsumes hydrogen or not. The product from the deoxygenation reactionsincludes a liquid portion and a gaseous portion. The liquid portionpresent in the deoxygenation effluent 44 includes hydrocarbon compoundsthat are largely normal paraffin compounds (n-paraffins) having a highcetane number. The gaseous portion includes hydrogen, carbon dioxide(CO₂), carbon monoxide (CO), water vapor, propane, and perhaps sulfurcomponents such as hydrogen sulfide. It is possible to separate andcollect the liquid portion (the hydrocarbons including n-paraffins) as adiesel fuel product without further reactions. However, in mostclimates, at least a portion of the liquid n-paraffins can be isomerizedto produce branched paraffins, which improves the cold flow propertiesof the fuel.

In an exemplary embodiment, the deoxygenation effluent 44 passes to anoptional hot separator 46 downstream from the deoxygenation reactionzone 40. One purpose of the hot separator 46 is to separate at leastsome of the gaseous portion from the liquid portion of the deoxygenationeffluent 44. Much of the gaseous portion, including the recoveredhydrogen, exits the hot separator 46 in a hot separator overhead stream48, and the liquid portion exits the hot separator in a hot separatorbottoms stream 50. The separated hydrogen is recycled back to thedeoxygenation reaction zone 40 in some embodiments, as described morefully below. The liquid hydrocarbons including the n-paraffins exit thehot separator 46 in the hot separator bottoms stream 50.

In some embodiments, water, CO, CO₂, and any ammonia or hydrogen sulfideare stripped in the hot separator 46 using hydrogen. In some embodiments(not shown), additional hydrogen is used as the stripping gas, but othergases could also be used. The temperature is controlled to achieve thedesired separation, and the pressure can be maintained at approximatelythe same pressure as the deoxygenation reaction zone 40 and theisomerization reaction zone (described below) to minimize bothinvestment and operation costs. Energy is required to change thetemperature or pressure, which increases operating costs, and additionalequipment is needed to enable the process to change the temperature ofpressure, which increases the investment cost. The hot separator 46 maybe operated at conditions ranging from a pressure of about 690 kPaabsolute (100 psia) to about 13,800 kPa absolute (2,000 psia), and atemperature of about 40° C. to about 350° C. In another embodiment, thehot separator 46 may be operated at conditions ranging from a pressureof about 1,380 kPa absolute (200 psia) to about 6,900 kPa absolute(1,000 psia), or about 2,410 kPa absolute (350 psia) to about 4,880 kPaabsolute (650 psia), and a temperature of about 50° C. to about 350° C.

The paraffinic components of the hot separator bottoms stream 50 areprimarily n-paraffins which range from about 8 to about 24 carbon atomsdepending on the type of renewable feedstock 10 used. Differentrenewable feedstocks 10 will result in different distributions ofparaffins. The hot separator bottoms stream 50 is divided andtransferred to various locations in different embodiments. A portion ofthe hot separator bottoms stream 50 may be recycled and added to theguard bed 26 at various locations, and to the deoxygenation reactionzone 40 at various locations, as described above. In alternateembodiments, other streams or no streams are recycled in place of thehot separator bottoms stream 50.

In an exemplary embodiment, the hot separator bottoms stream 50 alsoflows to an enhanced hot separator 52 to further separate the gaseousand liquid components of the deoxygenation effluent 44. Additional gasesare removed from the liquid hydrocarbons with the n-paraffins, and thegases are vented in an enhanced hot separator overhead stream 54, whichis combined with the hot separator overhead stream 48. The enhanced hotseparator 52 operates at similar conditions as the hot separator 46. Theenhanced hot separator operating conditions range from a pressure ofabout 690 kPa absolute (100 psia) to about 13,800 kPa absolute (2,000psia), and a temperature of about 40° C. to about 350° C. In anotherembodiment, the enhanced hot separator 52 may be operated at conditionsranging from a pressure of about 1,380 kPa absolute (200 psia) to about6,900 kPa absolute (1,000 psia), or about 2,410 kPa absolute (350 psia)to about 4,880 kPa absolute (650 psia), and a temperature of about 50°C. to about 350° C.

An enhanced hot separator bottoms stream 56 flows from the enhanced hotseparator 52 downstream to a first isomerization reaction zone 60. Theenhanced hot separator bottoms stream 56 is primarily made up of theliquid hydrocarbons, including the n-paraffins, from the deoxygenationreaction zone 40. Fresh hydrogen is added to the enhanced hot separatorbottoms stream 56 from a hydrogen feed line 36, so additional hydrogenis fed to the first isomerization reaction zone 60. In otherembodiments, the hydrogen could be fed to the first isomerizationreaction zone 60 in other manners, such as from a feed line pipeddirectly into a reactor in the first isomerization reaction zone 60.

Isomerization can be carried out in a separate bed of the same reactorused in the deoxygenation reaction zone 40, or the isomerization can becarried out in a separate isomerization reactor 58. For ease ofdescription, the following will address the embodiments where a separatereaction zone is employed for the first isomerization reaction zone 60.In an exemplary embodiment, the first isomerization reaction zone 60includes an isomerization catalyst 62 positioned within an isomerizationreactor 58, and is operated at isomerization conditions. Thehydrocarbons with the n-paraffins in the enhanced hot separator bottomsstream 56 are contacted with the isomerization catalyst 62 in thepresence of hydrogen to convert at least some of the n-paraffins intobranched paraffins. Only minimal branching is required to overcome thepoor cold-flow characteristics of the n-paraffins used in diesel or jetfuel. In some embodiments, the predominant isomerized paraffin productis a mono-branched hydrocarbon, because process conditions that producesignificant branching also increase the risk of excessive cracking thatreduces the yield of diesel or jet fuel. The hydrocarbons used in dieseland jet fuel generally have more carbons than the hydrocarbons used ingasoline, on average, and have a higher average boiling point. Besidesimproving the cold flow properties of diesel fuel, branched paraffinsalso increase the octane rating of gasoline fuels.

An isomerization effluent 64, which exits the first isomerizationreaction zone 60, is a hydrocarbon stream rich in branched paraffins. Bythe term “rich” it is meant that the isomerization effluent 64 has agreater concentration of branched paraffins than the stream entering thefirst isomerization reaction zone 60, and in some embodiments includesgreater than 50 mass percent branched paraffins. The isomerizationeffluent 64 may contain 70, 80, or 90 mass percent branched paraffins insome embodiments, but lower concentrations of branched paraffins arepresent in other embodiments. The degree of isomerization can be changedby adjusting the isomerization conditions. For example, a lower reactortemperature will decrease the degree of isomerization, and also decreasethe degree of cracking in the first isomerization reaction zone 60.

The isomerization of the n-paraffins can be accomplished by using avariety of suitable catalysts. The first isomerization reaction zone 60includes one or more beds of isomerization catalyst 62, and the catalystbeds can be in series and/or parallel. A single isomerization reactor 58may include one or more catalyst beds, so the first isomerizationreaction zone 60 can also include one or more isomerization reactors 58.In some embodiments, the first isomerization reaction zone 60 isoperated in a co-current mode of operation. Fixed bed trickle down flowor fixed bed liquid upward flow modes are both suitable. In someembodiments, the isomerization catalyst 62 is not sulfided, so nosulfiding agents are added to streams entering the first isomerizationreaction zone 60 downstream from the deoxygenation reaction zone 40. Inalternate embodiments, the isomerization catalyst is sulfided.

Suitable isomerization catalysts 62 include a metal of Group VIII (IUPAC8-10) of the Periodic Table and a support material. Suitable Group VIIImetals include platinum and palladium, each of which may be used aloneor in combination. The support material may be amorphous or crystalline,and many different support materials can be used. Suitable supportmaterials include, but are not limited to, amorphous alumina, amorphoussilica-alumina, ferrierite, metal aluminumsilicophosphates, laumontite,cancrinite, offretite, the hydrogen form of stillbite, the magnesium orcalcium form of mordenite, and the magnesium or calcium form ofpartheite, each of which may be used alone or in combination. Manynatural zeolites, such as ferrierite, that have an initially reducedpore size can be converted to forms suitable for olefin skeletalisomerization by removing associated alkali metals or alkaline earthmetals by ammonium ion exchange and calcination to produce a substantialhydrogen form. The isomerization catalyst 62 may also include one ormore modifiers, such as those selected from the group of lanthanum,cerium, praseodymium, neodymium, samarium, gadolinium, terbium, andmixtures thereof

The isomerization reaction occurs when hydrocarbons pass through theisomerization catalyst 62 at isomerization conditions. Isomerizationconditions include a temperature of about 150° C. to about 420° C. and apressure of about 1,720 kPa absolute (250 psia) to about 4,720 kPaabsolute (700 psia). In another embodiment, the isomerization conditionsinclude a temperature of about 300° C. to about 360° C. and a pressureof about 2,400 kPa absolute (350 psia) to about 3,800 kPa absolute (550psia). Other operating conditions for the first isomerization reactionzone 60 can also be used.

The hydrocarbons with the branched paraffins in the isomerizationeffluent 64 are processed through one or more separation steps to obtaina hydrocarbon stream useful as a fuel, and the separation steps vary indifferent embodiments. The isomerization effluent 64 includes both aliquid component and a gaseous component, various portions of which canbe recycled, so multiple separation steps may be employed. For example,in some embodiments the isomerization effluent 64 is separated in anisomerization effluent separator 66 positioned downstream from the firstisomerization reaction zone 60. Hydrogen exits the isomerizationeffluent separator 66 in an isomerization effluent separator overheadstream 68, and the liquid portion exits in an isomerization effluentseparator bottoms stream 70. The isomerization effluent separatoroverhead stream 68 is fed to the enhanced hot separator 52 in someembodiments, so the gaseous portions are combined with the gases in theenhanced hot separator overhead stream 54. In other embodiments (notshown), the isomerization effluent separator overhead stream 68 bypassesthe enhanced hot separator 52 and is eventually used as recycledhydrogen or processed in other ways.

Suitable operating conditions of the isomerization effluent separator 66include, for example, a temperature of about 280° C. to about 360° C.and a pressure of about 4,100 kPa absolute (600 psia), but otheroperating conditions are also possible. If there is a low concentrationof carbon oxides, or the carbon oxides are removed, the hydrogen may bedirectly recycled and re-used in the process. Hydrogen is a reactant inthe deoxygenation reaction zone 40 and the first isomerization reactionzone 60, and different renewable feedstocks 10 will consume differentamounts of hydrogen. Additional hydrogen can be added for feeds thatconsume more hydrogen. Furthermore, at least a portion of theisomerization effluent separator bottoms stream 70 can be recycled tothe first isomerization reaction zone 60 (not shown) to increase thedegree of isomerization, to aid in temperature control, or for otherpurposes.

The remainder of the isomerization effluent separator bottoms stream 70still has liquid and gaseous components and can be cooled by varioustechniques, such as air cooling or water cooling. The liquid portion ofthe isomerization effluent separator bottoms stream 70 is hydrocarbons,including the branched paraffins, as well as some n-paraffins that werenot isomerized into branched paraffins. After cooling, the isomerizationeffluent separator bottoms stream 70 is passed to a cold separator 72where the liquid component is separated from the gaseous component. Thehot separator overhead stream 48 and the enhanced hot separator overheadstream 54 are also fed to the cold separator 72, and can be combinedwith the isomerization effluent separator bottoms stream 70 upstreamfrom the cold separator 72. Suitable operating conditions of the coldseparator 72 include, for example, a temperature of about 40° C. toabout 60° C. (about 100° F. to about 140° F.) and a pressure of about3,800 kPa absolute to about 5,300 kPa absolute (about 550 to about 770psia), but other operating conditions are also possible. A waterbyproduct stream is also separated in the cold separator 72 (not shown).A cold separator overhead stream 74 and a cold separator bottoms stream76 exit the cold separator 72.

The cold separator overhead stream 74, or the gaseous componentsseparated in the cold separator 72, is mostly hydrogen and the carbondioxide from the decarboxylation reaction. Other components such as CO,propane, and hydrogen sulfide or other sulfur containing components maybe present as well. Water, CO, and CO₂ can negatively impact thecatalyst performance in the first isomerization reaction zone 60. It isdesirable to recycle the hydrogen, but if the CO₂ and other componentsare not removed, their concentrations can build up and negatively affectthe operation of the first isomerization reaction zone 60. A recoverygas cleaner 78 can be used to increase the purity of the cold separatoroverhead stream 74. The carbon dioxide can be removed from the hydrogenby several different processes, including but not limited to absorptionwith an amine, reaction with a hot carbonate solution, pressure swingabsorption, etc. If desired, essentially pure carbon dioxide can berecovered by regenerating the spent absorption media. A sulfurcontaining component, such as hydrogen sulfide, may also be present. Thesulfur containing component may be used to help control the relativeamounts of the decarboxylation reaction and the hydrogenation reactionin the deoxygenation reaction zone 40. The amount of sulfur is generallycontrolled, so the sulfur is also removed before the hydrogen isrecycled. Various methods can be used, such as absorption with an amineor a caustic wash, and the carbon dioxide and sulfur containingcomponents (as well as other components) are removed in a singleseparation step in some embodiments.

A recycle hydrogen stream 80 exits the recovery gas cleaner 78 after theimpurities have been removed. A recycle hydrogen compressor 82 urges thehydrogen back into the process. As discussed above, the recycle hydrogenstream 80 may be fed into the renewable feedstock feed stream 18, butthe recycle hydrogen stream 80 could be routed into the process in otherlocations as well, such as routed directly into the reactors of thedeoxygenation reaction zone 40 or the first isomerization reaction zone60. The recycle hydrogen stream 80 supplies the hydrogen for the guardbed 26 and the deoxygenation reaction zone 40, as discussed above.

The cold separator bottoms stream 76, or the liquid component separatedin the cold separator 72, contains the liquid hydrocarbons with thebranched paraffins useful as jet fuel and/or diesel fuel, as well assmaller amounts of naphtha, liquid propane gas (LPG), and otherhydrocarbons. The cold separator bottoms stream 76 may be recovered asdiesel boiling range fuel or it may be further purified in afractionation zone 84 that fractionates the various components of thecold separator bottoms stream. In one embodiment, the fractionation zone84 includes a product stripper 86 or a product fractionator (not shown)that can be operated, for example, with a vapor temperature of fromabout 20° C. to about 200° C. and a pressure from about 0 kPa (0 psia)to about 1,380 kPa absolute (200 psia) at the overhead of the productstripper 86. In alternate embodiments, the fractionation zone 84includes a plurality of fractionators and/or separators to divide thecold separator bottoms stream 76 into various fractions. Thefractionation zone 84 separates the cold separator bottoms stream 76into a fractionation zone overhead stream 88, a naphtha product thatexits the fractionation zone 84 at a naphtha outlet 92, and afractionation zone bottoms stream 94. The naphtha outlet 92 is splitinto a naphtha fraction 90 that is collected as a product, and a naphthareisomerization stream 93.

The fractionation zone overhead stream 88 includes LPG and lighterhydrocarbons, such as ethane or methane, and it may include butanes. Thefractionation zone overhead stream 88 can be further fractionated andsold as a product, used as a fuel gas, or used in other processes suchas the feed to a hydrogen production facility, a co-feed to a reformingprocess, or a fuel blending component. The fractionation zone bottomsstream 94 can be used a diesel range fuel or further fractionated andused as a jet fuel. The naphtha fraction 90 includes hydrocarbons withabout 5 to 8 carbon atoms, and boils from about 20° C. to about 150° C.,where the hydrocarbons are primarily a mixture of n-paraffins andbranched paraffins. In some embodiments, the naphtha is lightlyisomerized after making one pass through an isomerization reactor 58, soit includes relatively few branched paraffins. The naphtha fraction 90can be used as a component in gasoline, but it has an octane value ofabout 60 to about 70 after a single pass through the isomerizationreactor 58, so a higher octane value would increase the value of thenaphtha fraction 90 for use in gasoline. Most gasoline sold commerciallyhas an octane value of about 85 to about 95. The octane value can beincreased by converting n-paraffins into branched paraffins.

In an exemplary embodiment, some of the naphtha product from the naphthaoutlet 92 is further isomerized to convert n-paraffins into branchedparaffins by routing the naphtha reisomerization stream 93 back to thefirst isomerization reaction zone 60. Some of the naphtha product isremoved from the process in a naphtha fraction 90 to prevent the naphthafrom building up in the system. The isomerization catalyst 62 in thefirst isomerization reaction zone 60 will crack some of the hydrocarbonsin the naphtha into smaller molecules, which decreases the yield of thefinal naphtha fraction 90. However, cracking of the hydrocarbons in thenaphtha is minimized by reducing the contact time with the isomerizationcatalyst 62 in the first isomerization reaction zone 60. The naphthareisomerization stream 93 may be added to the first isomerizationreaction zone 60 by coupling the naphtha outlet 92 to a side inlet 96 ofan isomerization reactor 58 in the first isomerization reaction zone 60,where the side inlet 96 is positioned with some of the catalyst bedupstream from the side inlet 96 and some of the catalyst bed downstreamfrom the side inlet 96. The position of the side inlet 96 can beadjusted to optimize the degree of isomerization of the naphtha with thedegree of cracking, and in some embodiments the naphtha reisomerizationstream 93 is coupled to the inlet of the isomerization reactor 58 andcontacted with the entire isomerization catalyst bed. A side inlet 96configured so the naphtha bypasses some of the isomerization catalyst 62also minimizes any dilution effect by the naphtha on the isomerizationof the hydrocarbons with n-paraffins in the enhanced hot separatorbottoms stream 56.

Reference is now made to the exemplary embodiment illustrated in FIG. 2,which begins with the cold separator bottoms stream 76. In thisembodiment, the fractionation zone 84 includes a product stripper 86with a fractionation zone overhead stream 88 and a fractionation zonebottoms stream 94. The fractionation zone overhead stream 88 is fed intoa light gas separator 98. A lean gas stream 100 exits the light gasseparator as a gas, and a light gas separator bottoms stream 102 exitsas a liquid. The light gas separator bottoms stream 102 from the lightgas separator 98 includes the LPG 104 and the hydrocarbons in thenaphtha fraction 118. The LPG 104 and hydrocarbons in the naphthafraction 118 (prior to isomerization) are further separated in adebutanizer 106 that produces the LPG 104 as an overhead stream and thenaphtha reisomerization stream 93 as a bottom stream. The naphthareisomerization stream 93 exits the debutanizer 106 at the naphthaoutlet 92. The debutanizer 106 can be operated, for example, at a vaportemperature of about 20° C. to about 200° C. and a pressure from about 0to about 2,760 kPa absolute (0 to 400 psia) at the debutanizer overhead,but other conditions are also possible.

The naphtha outlet 92 from the debutanizer 106 is coupled to anisomerization reactor 114 in a second isomerization reaction zone 110 tofurther isomerize the paraffins in the naphtha fraction 118. In someembodiments, the second isomerization reaction zone 110 includes anisomerization catalyst 116 and operates at isomerization conditions. Thesecond isomerization reaction zone 110 can be operated to match the feedfrom the naphtha outlet 92, and a suitable isomerization catalyst 116and isomerization conditions can be used. In an exemplary embodiment,the isomerization catalyst 116 includes about 0.01 to about 3 weightpercent of a metal on an inorganic oxide carrier, and includes a halideas a promoter. Suitable inorganic oxide carriers include alumina,silica, zirconia, magnesia, thoria, and combinations thereof, but othercarriers can also be used. Suitable metals include Ruthenium, Rhodium,Palladium, Osmium, Iridium, and Platinum, and the weight percent isdetermined based on the weight of the metal, regardless of the form ofthe metal on the carrier. The halide promoter is present at about 0.1 toabout 10 weight percent, and includes chlorides or other halides.Suitable isomerization conditions include a temperature from about 120°C. to about 200° C. (about 250° F. to about 400° F.), and pressures fromabout 2,400 kPa to about 3,800 kPa (about 350 PSIG to about 550 PSIG).

The second isomerization reaction zone 110 can be used in place of, orin conjunction with, a naphtha recycle through the first isomerizationreaction zone. The naphtha reisomerization stream 93 is the primary feedto the second isomerization reaction zone 110, so the size of theisomerization reactor 114 and catalyst bed, the quantity ofisomerization catalyst 116 used, and the isomerization conditions can beoptimized for the naphtha reisomerization stream 93. A secondisomerization reaction zone hydrogen line 112 can be used to introducehydrogen for the isomerization reaction. The naphtha fraction 118 thenexits the second isomerization reaction zone 110 with a higher level ofbranched paraffins than the feed to the second isomerization reactionzone 110. An optional separator (not shown) can be installed downstreamfrom the second isomerization reaction zone 110 to vent hydrogen andlight gases produced by cracking in the isomerization reactor 114, andthe vented hydrogen can be reused in a similar manner to the hydrogencollected in the hot separator overhead stream.

Reference is now made to FIG. 1 again. The exemplary embodimentsdescribed above include many optional processes, or processes that canbe modified or arranged in different manners. In a very simplified form,the renewable feedstock feed system 12 is coupled to the deoxygenationreaction zone 40, because the renewable feedstock 10 flows to thedeoxygenation reaction zone 40. The deoxygenation reaction zone 40 islikewise coupled to the first isomerization reaction zone 60, which iscoupled to the fractionation zone 84, even though several vessels orprocesses are positioned between the different zones. The naphtha isrecovered from the fractionation zone 84 and re-isomerized to increasethe concentration of branched paraffins. Several vessels and steps areused to recover and reuse hydrogen throughout the manufacturing process.

It should be appreciated that the embodiment or embodiments illustratedare only examples, and are not intended to limit the scope,applicability, or configuration of the application in any way. Rather,the foregoing detailed description will provide those skilled in the artwith a convenient road map for implementing one or more embodiments, itbeing understood that various changes may be made in the function andarrangement of elements described without departing from the scope asset forth in the appended claims.

1. A method of producing fuel from a renewable feedstock, the methodcomprising the steps of: deoxygenating the renewable feedstock in adeoxygenation reaction zone to produce hydrocarbons comprising normalparaffins; isomerizing the hydrocarbons comprising normal paraffins toproduce hydrocarbons comprising branched paraffins; fractionating thehydrocarbons comprising branched paraffins to produce a naphtha at anaphtha outlet; and isomerizing the naphtha from the naphtha outlet. 2.The method of claim 1 wherein isomerizing the hydrocarbons comprisingnormal paraffins further comprise isomerizing the hydrocarbonscomprising normal paraffins in a first isomerization reaction zone atisomerization conditions; and wherein isomerizing the naphtha furthercomprises isomerizing the naphtha in the first isomerization reactionzone.
 3. The method of claim 2 wherein isomerizing the naphtha furthercomprises adding the naphtha to the first isomerization reaction zonesuch that the naphtha bypasses a portion of an isomerization catalystpositioned within the first isomerization reaction zone.
 4. The methodof claim 2 wherein isomerizing the naphtha further comprises isomerizingthe naphtha in a second isomerization reaction zone.
 5. The method ofclaim 1 wherein isomerizing the naphtha further comprises isomerizingthe naphtha in a second isomerization reaction zone.
 6. The method ofclaim 1 wherein deoxygenating the renewable feedstock further comprisesdeoxygenating the renewable feedstock wherein the renewable feedstockcomprises glycerides or free fatty acids.
 7. The method of claim 1wherein deoxygenating the renewable feedstock further comprisesdeoxygenating the renewable feedstock wherein the renewable feedstockcomprises oil extracted from a plant or an animal.
 8. The method ofclaim 1 further comprising sulfiding a deoxygenation catalyst in thedeoxygenation reaction zone.
 9. The method of claim 1 furthercomprising: contacting the renewable feedstock with a guard bed catalystat pretreatment conditions.
 10. The method of claim 1 furthercomprising: pre-cleaning the renewable feedstock in a pre-cleaning zone.11. A method of producing fuel from a renewable feedstock, the methodcomprising the steps of: contacting the renewable feedstock with adeoxygenation catalyst to produce hydrocarbons comprising normalparaffins; contacting the hydrocarbons comprising normal paraffins withan isomerization catalyst to produce hydrocarbons comprising branchedparaffins; fractionating the hydrocarbons comprising branched paraffinsto produce a naphtha at a naphtha outlet; and isomerizing the naphthafrom the naphtha outlet.
 12. The method of claim 11 wherein contactingthe hydrocarbons comprising normal paraffins with the isomerizationcatalyst further comprises contacting the hydrocarbons comprising normalparaffins with the isomerization catalyst wherein the isomerizationcatalyst is within a first isomerization reaction zone; and whereinisomerizing the naphtha further comprises contacting the naphtha withthe isomerization catalyst in the first isomerization reaction zone. 13.The method of claim 12 wherein isomerizing the naphtha further comprisesadding the naphtha to an isomerization reactor at a side inlet of theisomerization reactor, wherein the isomerization catalyst is positionedwithin the isomerization reactor and wherein the side inlet ispositioned such that the naphtha bypasses some of the isomerizationcatalyst within the isomerization reactor.
 14. The method of claim 12wherein isomerizing the naphtha further comprises contacting the naphthawith the isomerization catalyst in a second isomerization reaction zone.15. The method of claim 11 wherein contacting the hydrocarbonscomprising normal paraffins with the isomerization catalyst furthercomprises contacting the hydrocarbons comprising normal paraffins withthe isomerization catalyst wherein the isomerization catalyst is withina first isomerization reaction zone; and wherein isomerizing the naphthafurther comprises isomerizing the naphtha in a second isomerizationreaction zone different than the first isomerization reaction zone. 16.The method of claim 11 wherein contacting the renewable feedstock withthe deoxygenation catalyst further comprises contacting the renewablefeedstock with the deoxygenation catalyst wherein the renewablefeedstock comprises glycerides or free fatty acids.
 17. The method ofclaim 11 wherein contacting the renewable feedstock with thedeoxygenation catalyst further comprises contacting the renewablefeedstock with the deoxygenation catalyst wherein the renewablefeedstock comprises oil extracted from a plant or an animal.
 18. Themethod of claim 11 further comprising sulfiding the deoxygenationcatalyst.
 19. The method of claim 1 further comprising: pre-cleaning therenewable feedstock in a pre-cleaning zone.
 20. A system for producingfuel from a renewable feedstock comprising; a renewable feedstock feedsystem; a deoxygenation reaction zone coupled to the renewable feedstockfeed system; a first isomerization reaction zone coupled to thedeoxygenation reaction zone; a fractionation zone coupled to the firstisomerization reaction zone, wherein the fractionation zone comprises anaphtha outlet; and an isomerization reactor, wherein the naphtha outletis coupled to the isomerization reactor.